There are a great many prior art proposals for using telephone lines for automatic reporting of meter and status data as well as for control of clocks and the time of telephone calls and the reporting of alarm conditions and other remote metering and control applications. In many of the proposals for using telephone lines, an interrogation signal is sent from a receiving station to a reporting station to initiate the sending of a report, the receiving station being either at a telephone exchange or being connected through a telephone line thereto. Such systems may involve ringing of the customer's telephone or the installation of special ring-suppress equipment at the customer's facility or, alternatively, special equipment at the telephone exchange.
In another type of system, a reporting station initiates the making of a report. For example, the Stonor U.S. Pat. No. 3,098,123 discloses a system in which a pulse-dialing operation is automatically performed, followed by the sending of a message to report the condition at the reporting station. The Diaz U.S. Pat. No. 3,357,011 discloses a system in which the call-in time is controlled by a clock at the reporting station, the clock being also usable to trigger periodically transfers of data to a local memory for later transmission to the receiving station upon command.
In addition to the Diaz patent, there are other systems in which calls are made periodically or at preset times, including the Breen U.S. Pat. No. 3,046,339, the Jackson U.S. Pat. No. 3,294,910, the Klein U.S. Pat. No. 3,510,591, the Lindstrom U.S. Pat. No. 4,056,684, the Bocchi U.S. Pat. No. 4,086,434 and the Martin et al U.S. Pat. No. 4,104,486. In the Klein system, call time data are sent to a station to be stored in a memory and to be compared with clock signals to make a call-back at a desired time. The Vittoz U.S. Pat. No. 4,020,628 and the Emile, Jr. U.S. Pat. No. 4,125,993 illustrate systems in which signals may be transmitted through a telephone line to regulate the frequency or set the time at a remote clock or watch.
The National Weather Service of the National Oceanic Atmospheric Administration of the U.S. Department of Commerce has been a leader in the development of automated systems using telephone lines for the reporting of meter data. In a paper entitled: "AUTOMATIC HYDROLOGIC OBSERVING SYSTEM" by J. W. Schiesl, presented at the International Seminar on organization and operation of hydrological services, Ottawa, Canada, July 15, 1976, an "AHOS" system is described in which an Automatic Data Acquisition System (ADAS) includes a computer which operates on a standard interrogation cycle to collect data. Periodically, once every six hours, the ADAS transmits the data to a receiving station or user such as a River Forecast Center or a Weather Service Forecast Office. The system is such that a user may have the capability to request a special interrogation cycle which can be at optional intervals other than the standard cycles and to request the type of data to be reported when the ADAS reports in at the special requested time.
The computer and microprocessor technology, of course, developed very rapidly and since about the mid 1970's, microprocessors have been commercially available at relatively low cost to perform many complex functions. In addition, restrictions on the connection of equipment to telephone lines were removed in about the first half of the decade of the 1970's.
However, there has been no extensive use of telephone lines for automatic reading of water, gas and electric meters or the like. Those systems which have been used have been quite complicated and expensive and their use has been limited to special applications such as the monitoring of the meters of large industrial users of electricity or the performance of surveys on a random basis.